The present invention generally relates to methods and apparatus for polishing or planarizing workpieces such as semiconductor wafers. More particularly, the present invention relates to methods and apparatus for conditioning polishing pads used for the planarization of workpieces. The present invention is also directed to methods and apparatus for the planarization of workpieces which utilizes diamond brazed conditioning rings having a titanium nitride based coating or a coating comprising a thin film diamond deposition.
The production of integrated circuits began with the creation of high-quality semiconductor wafers. During the wafer fabrication process, the wafers may undergo multiple masking, etching and dielectric and conductor deposition processes. Because of the high-precision required in the production of these integrated circuits, an extremely flat surface is generally needed on at least one side of the semiconductor wafer to ensure proper accuracy and performance of the microelectronic structures being created on the wafer surface. As the size of the integrated circuits continues to decrease and the density of the microstructures per integrated circuit increases, the need for precise wafer surfaces becomes more important. Therefore, between each processing step, it is usually necessary to polish or planarize the surface of the wafer to obtain the flattest surface possible.
For a discussion of chemical mechanical planarization (CMP) processes and apparatus, see, for example, Arai, et al., U.S. Pat. No. 4,805,348, issued February, 1989; Arai, et al., U.S. Pat. No. 5,099,614, issued March, 1992; Karlsrud et al.,U.S. Pat. No. 5,329,732, issued July, 1994; Karlsrud, U.S. Pat. No. 5,498,196, issued March, 1996; and Karlsrud et al., U.S. Pat. No. 5,498,199, issued March, 1996.
Such polishing is well known in the art and generally includes attaching one side of the wafer to a flat surface of a wafer carrier or chuck and pressing the other side of the wafer against a flat polishing surface. In general, the polishing surface comprises a horizontal polishing pad that has an exposed abrasive surface of, for example, cerium oxide, aluminum oxide, fumed/precipitated silica or other particulate abrasives. Polishing pads can be formed of various materials, as is known in the art, and which are available commercially. Typically, the polishing pad may be a blown polyurethane, such as the IC and GS series of polishing pads available from Rodel Products Corporation in Scottsdale, Ariz. The hardness and density of the polishing pad depends on the material that is to be polished.
During the polishing or planarization process, the workpiece (e.g. wafer) is typically pressed against the polishing pad surface while the pad rotates about its vertical axis. In addition, to improve the polishing effectiveness, the wafer may also be rotated about its vertical axis and oscillated back and forth over the surface of the polishing pad. It is well known that polishing pads tend to wear unevenly during the polishing operation, causing surface irregularities to develop on the pad. To ensure consistent and accurate planarization and polishing of all workpieces, these irregularities should either be removed or accounted for.
One method of removing the surface irregularities which develop in the polishing pad is to condition or dress the pad with some sort of roughing or cutting means. Generally this truing or dressing of the polishing pad can occur either while the wafers are being polished (in-situ conditioning), or between polishing steps (ex-situ conditioning). An example of ex-situ conditioning is disclosed in Cesna, et al., U.S. Pat. No. 5,486,131, issued on Jan. 23, 1996, and entitled Device for Conditioning Polishing Pads. An example of in-situ conditioning is disclosed in Karlsrud, U.S. patent application Ser. No. 08/487,530, filed on Jul. 3, 1995, and entitled Polishing Pad Conditioning. Both the Cesna, et al. patent and the Karlsrud application are herein incorporated by reference.
Generally, in the semiconductor wafer polishing and planarization context small roughing or cutting elements, such as diamond particles, are used to condition the polishing pads. As shown in both the Cesna, et al, patent and the Karlsrud application, both in-situ and ex-situ conditioning apparatus utilize circular ring conditioners which have these cutting elements secured to a bottom flange of the ring. Generally, these cutting elements are secured to the bottom surface of the flange of the carrier ring by an electroplating process or brazing process. Electroplating produces a simple mechanical entrapment of the cutting elements on the carrier ring by depositing metal, for example in a layer-by-layer fashion around the cutting elements until they are entrapped. However, one problem with the electroplating process is that the electroplating bond holding the cutting elements to the ring surface is relatively weak and the cutting elements occasionally become dislodged from the conditioning ring and embedded in the polishing pad. Further, because the electroplating bond is susceptible to shearing forces, a substantial amount of bonding material is needed to hold the cutting elements in place. As a result, the bonding material actually covers most, if not all, of the many cutting elements, thereby, comprising the conditioning capacity of the conditioning ring. Thus, the previously mentioned brazing process is preferred. A detailed discussion of the brazing process is discussed herein as well as in Holzapfel, et al., U.S. patent application Ser. No. 08/683,571, filed Jul. 15, 1996, which is herein incorporated by reference.
The cutting elements which are secured to the bottom surface of the flange of the carrier rings may comprise diamonds, polycrystalline chips/slivers, silicon carbide particles, and the like. However, regardless of whether the conditioning rings are braze plated or electroplated in order to retain the cutting elements, such as diamonds, these processes are not ideal in that they exhibit a very short lifetime which results in diamond loss, diamond fracture, or plating wear. As previously indicated, these lost or fractured diamonds can cause severe scratches in the wafers that are being polished. Wafers that are scratched are considered to be scrap and this can result in increased costs to the consumer. Further, the short lifetime of the conditioning rings due to plating wear is significant in that the conditioning rings are typically the most expensive consumable component part on the CMP apparatus.
Although the brazing of the cutting elements to secure them to the carrier ring is preferable over the electroplating process, there are still some problems associated with the brazing process. The problems associated with the unreliability of the bond created using brazed diamond technology in various applications has been addressed in the prior art. For example, in Kapoor et al., U.S. Pat. No. 5,567,525, the reliability of a braze joint formed between a diamond film and a tungsten carbide object is increased by covering the diamond film with a braze comprising vanadium. Further, a method for utilizing high temperature and high pressure to form a polycrystalline composite compact having reduced abrasive layer stresses is disclosed in U.S. Pat. No. 5,560,754 issued to Johnson et al. Also, U.S. Pat. No. 4,899,922, issued to Slutz et al., describes a brazed implement having a thermally stable polycrystalline diamond with shear strengths exceeding about 50 kpsi even while furnace cycling the brazed implements. This is achieved by brazing the compact to another compact or to a cemented carbide support using a brazing alloy containing an effective amount of chromium and having a liquidus above about 700 degrees C. Still, each of these methods for creating a more reliable brazed bond requires substantial mechanical and/or chemical manipulation including a temperature application. Further, none of these prior art patents suggests the use of their respective methods in a semiconductor processing capacity, particularly in the conditioning of conditioning rings used in that application process.
Accordingly, there is a need for an improved method and apparatus for conditioning polishing pads used in the polishing or planarization of semiconductor wafers. More particularly, there is a need for a simple and efficient method and apparatus for conditioning the rings which are used for conditioning the polishing pads so that there is a decrease in diamond loss, diamond fracture and plating wear of the conditioning rings thereby resulting in a longer life for the conditioning rings and a decrease in cost to the end consumer utilizing semiconductor chips.
It is a principal object of the present invention to provide an improved method and apparatus for polishing or planarizing workpieces such as semiconductor wafers.
It is another object of the present invention to produce improved diamond brazed conditioning rings used for conditioning polishing pads in the planarization of workpieces.
It is still another object of the present invention to provide a method and apparatus for polishing workpieces which includes the coating of a conditioning ring used to condition the polishing pad such that fractures and losses of the cutting elements contained on the conditioning ring are significantly reduced.
It is yet another object of the present invention to provide an improved method and apparatus for polishing workpieces which results in less scrap, namely fewer scratched semiconductor wafers.
It is still a further object of the present invention to provide a method and apparatus for polishing workpieces which extends the lifetime of the conditioning rings used in apparatus which perform chemical mechanical planarization processes, thereby decreasing costs associated with polishing and planarizing workpieces.
In brief, the present invention provides methods and apparatus for conditioning polishing pad devices which overcome many of the shortcomings of the prior art. In accordance with one aspect of the present invention, a polishing pad conditioning device for conditioning a polishing pad by contact with the pad is configured with cutting elements, such as diamonds, braze bonded to its bottom surface, and a titanium nitride based coating or a thin film diamond deposition placed over the braze bonded surface. The conditioning device also suitably includes a means for engaging the conditioning means with the polishing pad and for rotating the conditioning means on, and oscillating the conditioning means over, the top surface of the polishing pad.
In accordance with a further aspect of the present invention, the engaging rotating and oscillating means comprises an operating arm adapted for moving the conditioning device into, and out of, operative engagement with the top surface of the pad, and for oscillating the conditioning device radially over the top surface of the pad. The conditioning device comprises a carrier element configured in the shape of a ring, and having cutting elements attached to the bottom surface of the carrier element in a circular ring configuration. Further, a coating of either a composition containing titanium nitride or a thin film diamond deposition is applied over the cutting elements.
In accordance with another aspect of the present invention, the carrier element may include a flange which extends about the periphery of the ring, with the cutting elements being attached to the flange.
In accordance with yet a further aspect of the present invention, the flange includes cut out portions to permit materials to escape from the interior of the carrier ring. In accordance with this aspect of the invention, the cutting elements are distributed substantially uniformly along the flange and the elements are braze bonded to the flange with a brazed metal alloy. Preferably, the brazed metal alloy will only cover about 25% to 75%, and preferably about 40-60%, and most preferably about 50% of the height of the cutting elements. For example, for cutting elements (e.g. diamond particles) having an average height (i.e., diameter) in the range of 50 to 200 micrometers and most preferably about 150 micrometers, the brazed metal alloy should preferably cover each cutting element up to about 50% of its height, or up to about 75 micrometers. Particle sizes in the range of 50 to 200 U.S. mesh, and most preferably about 100 to 120 U.S. mesh are particularly well adapted to the present invention.
In accordance with a further aspect of the present invention, covering less than 25% to 40% of the height of a cutting element with braze may result in an insufficiently secure bond, such that the cutting elements may break away from the braze, thereby liberating the cutting element and perhaps damaging the workpieces. On the other hand, covering the cutting elements with braze in excess of 60% to 80% of the height of the cutting element may impede the ability of the cutting elements to properly dress or condition a pad. Thus, the present inventor has determined that an optimal range involves covering the cutting elements in braze up to about 50% of the height of the cutting elements and then coating the brazed cutting elements with a composition having a titanium nitride base or a thin film diamond deposition.
In accordance with yet a further aspect of the present invention, the conditioning device may be configured to condition the polishing pad at the same time workpieces are being polished. In accordance with this aspect of the invention, the conditioning device preferably is configured to mount to a moveable carrier element, which holds the workpieces during polishing.
In accordance with a further aspect of the present invention, the conditioning device is ring figured to mount around the outer perimeter of the workpiece carrier element, wherein the cutting elements are securely attached to the bottom surface of the ring in a circular configuration via brazing of the cutting elements and a titanium nitride coating or a thin film diamond deposition is deposited over the brazed cutting elements.
In accordance with yet a further aspect of the present invention, the cutting elements may be attached to a flange which extends about the periphery of the ring. In addition, the flange preferably may include cut out portions to permit materials to escape from the interior of the ring.
In accordance with yet another aspect of the present invention, the cutting elements used may comprise different materials, such as, for example, diamond particles, polycrystalline chips/slivers, cubic boron nitrite particles, silicon carbide particles and the like. The coating element may comprise SUPERNEXUS, which is a tradename for a titanium nitride product, or a thin film diamond deposition. SUPERNEXUS is produced by GSEM, Inc. located in Beaverton, Oregon and comprises part titanium nitride and part zirconium nitride. Alternatively, the coating element may comprise a thin film diamond coating which consists of man-made diamond components, the bulk of which are comprised of carbon with a minimum of hydrogen. These diamond particles are made synthetically by heating carbon and a metal catalyst in an electric furnace at about 3000 degrees F. under high pressure.